1. Field of the Invention
This invention relates to a vehicle suspension system, and more particularly to a vehicle suspension system which includes a fluid cylinder and in which the suspension properties change with change in the amount of fluid introduced into the fluid cylinder.
2. Description of the Prior Art
As disclosed, for instance, in Japanese Patent Publication No. 59-14365, there has been known a socalled hyrdro-pneumatic suspension system which comprises fluid cylinders connected between the vehicle body and the respective wheels and a gas spring connected to each of the fluid cylinders.
Further, there has been known an active control suspension system in which the amount of fluid introduced into the fluid cylinder for each wheel is changed separately from the other fluid cylinders and the properties of which is changed according to the operating condition of the vehicle.
When such an active control suspension system is actually incorporated in a vehicle, fail-safe measures against a failure in the flow control system for controlling the amount of fluid introduced into the fluid cylinders or in various sensors should be taken.
As the fail-safe measures, immediate interruption of the control, warning and the like can be employed. However, it is preferred that suitable measure be selected according to the kind of the failure. That is, when the control is immediately interrupted for a failure which does not affect the nature of the control, the effect of the active suspension system, e.g., improvement in the driving performance, will be easily lost. On the other hand, just a warning is not sufficient in view of safety for a failure which affects the nature of the control occurs.